Summary
Free and keyless, with the reliability that implies — fine for exploration, not for anything that must not break.
yfinance scrapes endpoints Yahoo does not commit to, so it works well until Yahoo changes something and then it does not. That trade is right for research and wrong for a pipeline. What it buys you is immediacy: no signup, no key, no quota, so checking a ticker mid-conversation costs nothing. Treat a gap in the data as a possible library problem rather than a fact about the market.
What it is
A server exposing yfinance, the widely used Python library for Yahoo Finance data, as tools an assistant can call.
What you get
The functions yfinance provides — quotes, historical series and the fundamentals Yahoo publishes.
Requirements
Python with yfinance. No API key, since it uses Yahoo's public endpoints.